Sulfur arsenic—oxygen bonds

The most common valence states of arsenic are —3, 0, +3, and +5 (Shih, 2005), 86. The —3 valence state forms through the addition of three more electrons to fill the 4p orbital. In the most common form of elemental arsenic (As(0)), which is the rhombohedral or gray form, each arsenic atom equally shares its 4p valence electrons with three neighboring arsenic atoms in a trigonal pyramid structure ((Klein, 2002), 336-337 Figure 2.1). The rhombohedral structure produces two sets of distances between closest arsenic atoms, which are 2.51 and 3.15 A (Baur and Onishi, 1978), 33-A-2. The +3 valence state results when the three electrons in the 4p orbital become more attracted to bonded nonmetals, which under natural conditions are usually sulfur or oxygen. When the electrons in both the 4s and 4p orbitals tend to be associated more with bonded nonmetals (such as oxygen or sulfur), the arsenic atom has a +5 valence state. 

Evidence for exchange of arsenic-carbon with arsenic-oxygen and arsenic-sulfur bonds, respectively, is obtained from the thermal dispor-portionation of methylarsenous oxide (143) according to Eq. (154), of phenyl-arsenous oxide according to Eq. (155), and of alkyl or arylarsenous sulfides according to Eq. (156). 

Only for a few organozinc compounds, in which in addition to the zinc-carbon bond a zinc-heteroatom bond other than oxygen or nitrogen is present, have structures in the solid state been determined. These structures include those of organozinc compounds in which, in addition to the zinc-carbon bond, a zinc-sulfur, zinc-selenium, zinc-phosphorus or zinc-arsenic bond is present. 

The SRN1 process has proven to be a versatile mechanism for replacing a suitable leaving group by a nucleophile at the ipso position. This reaction affords substitution in nonactivated aromatic (ArX) compounds, with an extensive variety of nucleophiles ( u ) derived from carbon, nitrogen, and oxygen to form new C—C bonds, and from tin, phosphorus, arsenic, antimony, sulfur, selenium, and tellurium to afford new C-heteroatom bonds. 

---